1. Technical Background
The present invention relates generally to materials and methods for medical devices.
2. Discussion
A variety of polymers are used to make many different medical devices, including catheters, sheaths, grafts, balloons, catheter sheath introducers, and other medical devices used in the body of a patient. Such polymers used for medical devices include nylons, polyethylenes, polyesters, polyurethanes, and polyamides.
Several desirable features for such polymers include in particular flexibility and low friction, as well as strength, the capability of being produced in a range of different flexibilities, and column stiffness.
Of the polyamide materials, polyamide-12 in the form of a homopolymer has been used for a variety of medical devices, some types of which are referred to as nylon-12. Another material in the polyamide family that has been used includes polyamide-12 in a copolymer with other materials, including polyether block amide (PEBA). Also, polyamide-12 may be blended with PEBA to produce a material having a desired flexibility for a given application. However, PEBA generally has physical properties that are less than optimal for certain applications, including relatively high friction, a relatively high level of gels, and the absence of amide functional groups when the material is made with relatively high flexibility or low durometers.
Another example is polyamide made in a coextrusion with high-density polyethylene (HDPE), which results in a multiple layer device. U.S. Pat. No. 5,538,510 describes multilayer coextrusions of polyamides with high-density polyethylene. The resulting structure has relatively low friction on the high-density polyethylene layer, while the polyamide layer can be bonded to other polyamide materials by application of heat and pressure. It is desirable to develop such a material having these properties that is available for certain applications in a selective range of flexibilities.
The materials of the present invention provide a unique combination of physical properties that are advantageous for use in medical devices for maneuvering through the circulatory system. The properties of high-strength, capability of bonding to other polyamides, and kink resistance are retained. In addition, several physical properties and benefits are provided by the materials of the present invention, including low friction, functional groups to bond to low friction surfaces, a range of flexibilities, and low gel counts.
Accordingly, the materials of the present invention preferably include blends of polyamide and maleated polyethylene. The polyamide component of the blended materials of the present invention may of course include both homopolymers and copolymers, of which the copolymer is preferred.
More particularly, this copolymer preferably uses disruption of the crystallinity of the polyamide to increase flexibility to a desired level. This method of increasing flexibility is in contrast to and more effective than PEBA, for example, which is also a copolymer. Instead of crystalline disruption, PEBA uses flexible linkages for flexibility.
The other component of the polymers of the present invention, maleated polyethylene, is preferably HDPE, with the addition of the maleic anhydride.
Preferably, the polyethylene component of the blended polymers of the present invention is as described in U.S. Pat. No. 5,538,510, entitled xe2x80x9cCatheter Having Coextruded Tubing,xe2x80x9d issued to Fontirroche, et al. on Jul. 23, 1996, which is incorporated by reference. More specifically, the preferred polyethylene component of the blended polymer materials of the present invention is high-density polyethylene modified with maleic anhydride.
As an example, the present invention will be described in relation to medical devices, and more particularly to medical catheters. However, it should be understood that the present invention relates to any apparatus or method having the features of the present invention, and is not limited to a particular material or type of design.